The role of rainwater-borne hydrogen peroxide in the release of arsenic from arsenopyrite

•Arsenopyrite weathering was markedly complicated by H2O2 in the synthetic rainwater solutions.•Arsenic release was enhanced by H2O2 at the concentration range set in the experiment.•H2O2 played an indirect role in the transformation of arsenite into arsenate in the solution.•Fate of liberated arsenic species may be affected due to the formation of FeAsO4 precipitates.•This sheds some light on a previously overlooked natural process worthy of further investigation. A microcosm experiment was conducted to examine the effects of hydrogen peroxide (at a concentration range of 5–50μM) on the release of arsenic from the dissolution of arsenopyrite, a dominant arsenic-bearing mineral occurring in natural environments. This was to simulate the reaction between rainwater-borne hydrogen peroxide and arsenopyrite grains exposed on the land surfaces during rainfall events. The results showed that the release of arsenic from arsenopyrite was enhanced by the H2O2 at this concentration range. It was also evident that H2O2 played an indirect role in the transformation of arsenite into arsenate in the solutions, which might affect the fate of the liberated arsenic species due to the formation of FeAsO4 precipitates. The preliminary study sheds some light on the possible role of rainwater-borne H2O2 in the weathering of arsenopyrite, which could complicate the geochemical processes governing the release, transport and fate of arsenopyrite-derived arsenic in natural environments. This provides a rationale for conducting additional laboratory-based investigations to obtain further insights into the chemical mechanisms and kinetics, and the subsequent field-scale study to validate the research findings.